Field of the Invention:
The invention relates to a device for guiding a strip in a liquid bath and is especially well suited for the continuous coating of a metal strip by hot dipping in a dip tank containing a bath of molten metal.
Processes of continuous lining of metal strips by going through a bath of molten metal have been known for a long time. For example, the strip which is coming as a spool can be unwound and subjected, in a continuous line, to a pickling then to an annealing under neutral atmosphere, in a heater at the exit of which the strip is immersed in a dip tank full of liquid metal, such as zinc or a zinc-aluminium alloy. To do that, the strip has to run on two successive diverting rollers, respectively an upper roller which diverts it downwards and a roller immersed in the bath of metal from which the strip goes back up and out of the bath according to a rather vertical direction, and then is conducted towards mangling and cooling devices. The strip, then, can be subjected to various finish treatments like a skin-pass and chemical treatments of surface before being spooled again.
Because of the rather high travelling speed of the strip, the diverting roller immersed in the bath is spinning at a rather high speed and, moreover, has to withstand the tension of the strip. Therefore it is supported by bearings that are subjected to important stresses and the life span of which is fairly limited. These bearings can be immersed in the bath or placed outside of it.
In the simplest assembly that is described, for example, in document FR-A-2735499, the diverting roller is supported by two bearings which are mounted on two aligned fixed trunnions supported by two vertical arms going into the bath. To improve the strength of the bearings immersed this way, their components can be made of ceramic or, for example, of a cobalt-based alloy. Such an assembly is interesting because of the great facility of removal of the roller but the life span of the bearings remains limited. Moreover, the insertion into the bath of the bearings and of the support arms requires a wider dip tank and therefore an increase of the volume of liquid metal.
Another possibility consists in mounting the bearings on the sidewalls of the dip tank which therefore must be equipped with sealing gaskets to avoid or, at least, to limit the leakages of liquid metal the pressure of which, at gasket level, can be rather important considering the metal density and the immersion depth of the roller.
For example, document JP-A-4346641 describes a gasket inside which a linear engine built in the wall determines an electromagnetic force of return of the metal towards the inside of the bath. However, the two axes of the roller which are extending between each end of it and the corresponding bearing necessarily have a certain length and therefore are subjected, because of the tension exerted on the strip, to transverse stresses which cause an off-centering of the roller axis regarding the hole of crossing in the sidewall and, thus, a risk of damage of the gaskets and of increase of metal leakages. This is why, in another assembly described in document FR-A-2 721 235 and concerning a dip tank of acid pickling of a metal strip, each axis of the roller crosses the sidewall of the dip tank and is supported by a bearing mounted on a second wall in spaced relation with the sidewall, said space wherein the possible leakages of liquid are collected. Document JP-A-10251819 describes a similar assembly for a galvanizing device and considers the heating of the liquid collected in the spout, to send it back in the bath. Such assemblies complicate the setting and, furthermore, increase again the distance between the bearing and the wall of the dip tank and, as a consequence, the length of the axis and the risks of its off-centering because of the transverse stresses exerted by the tension of the strip. Besides, if the roller has to be removed for maintenance or replacement, the hole of crossing of the axis is widely open and the dip tank has therefore to be drained beforehand.
Now, despite the fact the use of new materials may improve performance of the immersed rollers, these have still to be removed quite often and the outcome is a break of the running that decrease the plant productivity.
BRIEF SUMMARY OF THE INVENTION The invention brings a solution to such problems thanks to a new assembly of the support bearings of the axes of an immersed roller enabling, in particular, to ensure an excellent centering of the roller and, as a consequence, to decrease the risks of leakages. Furthermore, thanks to the invention, the operations of removal and of reassembly of the roller are much simpler than in the known assemblies and do not require a drain of the dip tank beforehand.
On another hand, the invention is designed especially for the coating of a strip with a liquid metal but could also be used each time a roller is immersed in a corrosive liquid or fluid, for example an acid or an electrolyte. Therefore the invention concerns, generally speaking, a device for guiding a strip in a bath of liquid contained in a dip tank, comprising a diverting roller immersed in the dip tank between two sidewalls of it and journalled for rotation around an axis in two aligned bearing shafts respectively crossing the two sidewalls of the dip tank, perpendicularly to said sidewalls, by passing through a hole of the wall and extending up to a support part rotating in a centering bearing placed outside the dip tank. According to the invention, each bearing of a shaft of the roller comprises at least two rotating support components mounted in a fixed housing and separated from each other in order to withstand transverse stresses exerted on the roller, respectively an external support component and an internal support component placed the closest as possible to the wall, the housing of the bearing being placed on a support plane surrounding the hole of crossing of the shaft and perpendicular to the axis of the hole, along an external side of the sidewall of the dip tank, said sidewall being supplied with means of centering of the housing around the axis of the hole of crossing of the shaft of the roller.
In a particularly advantageous fashion, each bearing shaft of the roller comprises an external part extending between two rotating support components, in spaced relation, of the bearing and an internal part crossing the sidewall of the dip tank and inserted with a small play inside a cylindrical opening built in the sidewall and delimiting the hole of crossing of the shaft.
This cylindrical opening extends on a length sufficient to place along said opening at least tightness means by production of a reverse flow towards the inside of the dip tank of the metal seeping in the annular space between the bearing shaft of the roller and the internal side of the cylindrical opening.
Various means can be used, separately or as a combination, to ensure this tightness.
For example, at least one helical groove can be designed along the internal part of the shaft inserted in the cylindrical opening.
Advantageously, the device comprises means of insertion of a fluid under pressure in the annular space resulting from the play between the internal part of the shaft and the cylindrical opening limiting the hole of crossing of the shaft, for the upholding of the tightness with leakage losses of the fluid at least towards the inside of the dip tank.
But, if the roller is immersed in a bath of liquid metal such as zinc, the sidewall of the dip tank can comprise at least induction means producing, around the cylindrical opening of crossing of the shaft, a magnetic field capable of determining a return towards the inside of the dip tank, of the metal infiltrated in the annular space between the shaft and the opening.
In case the sidewall of the dip tank is lined internally with a refractory coating, each shaft of the roller passes with a small rotation play through a hole of the sidewall and is extended up to an end side of the roller by an internal part inserted with a small play inside a cylindrical opening made through the whole thickness of the refractory coating of the wall.
According to another characteristic particularly advantageous, at least one of the two bearing shafts of the roller is fixed in a removable fashion, by an internal end, on a corresponding end side of the roller and is mounted for sliding axially in the cylindrical opening between a tightened position of bearing of the roller and a loosened position of removal of the roller. Preferably, the internal end of the shaft tightens in a removable fashion, by axial sliding, on a centering component built on the corresponding end side of the roller. To that purpose, the internal end of the shaft and the centering component of the roller can be supplied with complementary parts made respectively hollow and protruding in order to fit into one another by axial sliding.
Thus, for the removal of the roller, it is sufficient to laterally move apart the two bearing shafts which are remaining inserted in the holes crossing the walls and the openings that are extending them and it is not necessary to drain the dip tank, tightness remaining ensured. Advantageously, after the engagement of the internal end of the shaft on the centering component of the roller, said roller can be driven in rotation by means of exertion of a rotation torque on the external part of the shaft.
Preferably, the internal part of the shaft is coated on its outside with a material standing up to wear and/or to corrosion from the liquid contained in the dip tank, such as a ceramic material. In a preferred embodiment of the invention, the internal part of the shaft that is crossing the wall of the dip tank forms a centering pin mounted for sliding axially in a tightness piece shaped like a hollow socket having a cylindrical external side inserted with a small play inside the cylindrical opening of the sidewall and emerging inside the dip tank from an internal end sealed by a bottom supplied with a part engaging in a removable fashion on a centering component of the end side of the roller. In case of removal of the bearing and of the shaft, this socket can remain inserted inside the cylindrical opening of the sidewall in order to maintain tightness. Advantageously, the shaft is subjected, in use, to an axial load directed towards the inside and is leaning on the socket by means of a shoulder on the socket, for the engagement of the internal end of said socket on the centering component of the roller. 
Preferably, the tightness socket is made or, at least, coated on its outside of a material standing up to wear and/or to corrosion from the liquid contained in the dip tank, a ceramic for example and the cylindrical opening of crossing of the internal part of the shaft is built in a ring made of refractory material.
According to another characteristic particularly advantageous, the housing of the bearing is placed on a rigid fixture integrated into the sidewall of the dip tank and defining the support plane orthogonal to the axis of the hole of crossing of the shaft.
Preferably, the housing of the bearing forms, at its end facing the dip tank, a cylindrical head centred around the axis of the hole of crossing of the shaft and axially inserting itself in an internal boring of an edge of the support fixture surrounding the crossing hole and having a plane side perpendicular to said axis upon which is placed a plain clamp set around the head of the housing, said plane side defining the support plane.
According to another preferred characteristic, the housing of the bearing is fixed on the support fixture by elastic means enabling to exert an axial thrust stress capable of absorbing possible thermal stress. On another hand, in a preferred embodiment of the invention, the two rotating components of support of the external part of the shaft are mounted inside an external cage forming a cartridge inserted in an axial boring of the housing of the bearing and capable of being removed from the housing with the bearing by axial sliding while letting the housing fixed on the centering fixture. Furthermore, the centering of the shaft can be tuned by insertion of thin pieces of adaptable thickness between the cartridge bearing the shaft and a boring of the housing in which it is inserted.